The present invention relates to a radio equipment such as a mobile telephone employed in a mobile communication, a transmit power controlling method in the radio equipment, and a recording medium for recording a program to execute the transmit power controlling method.
In the mobile communication device such as the mobile telephone employed commonly, a function for controlling its own transmit power according to a distance between a base station and a mobile station in transmitting information is installed. In order to improve a frequency utilization efficiency by reducing interference between communication channels, transmit power control for keeping constant a power of the signal which can reach the base station is essential in a multiple access type communication system for multiplying a plurality of communication channels.
In particular, in the mobile communication device of CDMA (Code Division Multiple Access) system by using the spread spectrum technology, there is a high possibility that the so-called far-and-near problem is caused, and the interference with others must be suppressed to the lowest minimum. Therefore, transmit power control to enable a wide dynamic range (e.g., 70 to 80 dB) and high linearity is requested. In the wideband CDMA (W-CDMA) system which is examined now as a next generation mobile communication system, precision request of transmit power becomes higher in high power transmission and also transmit power control with higher precision is requested.
The transmit power control is classified into two types, i.e., "open loop control" in which an intensity of signal supplied from the base station is measured by the mobile station and then transmit power of the mobile station is adjusted based on measured results, and "closed loop control" in which the intensity of signal supplied from the mobile station is measured by the base station, then transmit power controlling data are transmitted from the base station to the mobile station based on measured results, and then a transmit power of the mobile station is adjusted according to the data. In the current mobile communication device, it is common that "power precision compensation control" is not executed wherein transmit power can be suppressed within a predetermined range relative to a target value in the mobile station in itself when the above transmit power control is effected, but merely "limiting control" is executed wherein transmit power can be suppressed not to exceed an allowable upper limit value of transmit power is effected.
However, according to the above radio equipment in the prior art, in the communication circumstances in which transmit power control of wide dynamic range and high linearity is needed, it has been difficult to assuring absolute precision of the transmit power (allowable error of the variable range in the transmit power control) while keeping power variable amount precision (allowable error of the power control target value) when the transmit power being output from the mobile station is controlled variably, so that sometimes it has been difficult to satisfy transmit power precision being specified by the radio law or regulation at the maximum power transmission. In addition, there is a possibility that, if the mobile station comes closest to the base station, the interference with others is increased. Further, it is possible to cause various disadvantages in practical use since the connection is easily disconnected if the mobile station goes farthest from the base station.